The correlation between chemically-induced immune defects and biochemical defects in lymphoid tissues (thymus, spleen, bone marrow) and specific-populations of lymphoid cells (pleuripotent stem cells, granulocyte-macrophage precursors, T-cells, B-cells, peritoneal and pulmonary, macrophages) were investigated in in vitro and in vivo studies. Rate limiting enzymes in the hexose monophosphate shunt, glycolysis and the tricarboxylic acid cycle, and marker enzymes in macrophages, have been assayed. Change in substrate flow through these biosynthetic pathways were caused by immunotoxic chemicals (mercuric chloride, methyl and ethyl carbamate, DES, asbestos) and tissue-specific pathway inhibition was correlated with functional defects in the immune system.